[Amps] Tube amps are not a thing of the past

[N1BUG]

I just cut the anode off a dud 4CX1000A. The control grid structure 
cannot be seen until I determine how to cut away the screen grid 
without destroying the control grid which I am going to guess is not 
far inside it.

I ran a 4CX1000A with 5 mA grid current on CW at 144 MHz for years. 
I don't know whether the tube was harmed in any way but this but 
performance never changed. I had it biased to near cutoff with only 
about 10 mA plate idling current, but I don't recall what the grid 
voltage was. I would guess somewhere around 75V. At 5 mA that's 
still not much grid dissipation!

Paul


On 06/05/2017 01:30 PM, Gary Schafer wrote:
> Hi Jim,
> I think that the 4CX1500 has the same grid as the 4CX1000.
> Somewhere I have seen it written by Eimac that it is ok to draw a small
> amount of grid current during brief tune up.
> 
> The Collins 30S-1 (4CX1000) develops ALC from grid current.
> 
> 73
> Gary  K4FMX
> 
>> -----Original Message-----
>> From: Amps [mailto:amps-bounces at contesting.com] On Behalf Of MU 4CX250B
>> Sent: Monday, June 05, 2017 11:03 AM
>> To: Jim Thomson
>> Cc: amps at contesting.com
>> Subject: Re: [Amps] Tube amps are not a thing of the past
>>
>> I've long wondered what the zero watt rating of the 4cx1000 grid
>> actually means. I've assumed it means the tube is rated for class AB1
>> operation only, and that the rating doesn't reflect the actual
>> physical limitation of the grid structure.  I wonder if anybody has
>> actually cut apart a tube and inspected the grid?
>> 73,
>> Jim w8zr


-- 
Paul
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